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itemtype="https://schema.org/Organization"><meta itemprop="name" content="Lizikang_Blog"></span><header class="post-header"><h1 class="post-title" itemprop="name headline">计算机网络笔记 第二章 物理层（1）</h1><div class="post-meta"><div class="post-time" style="display:inline-block"><span class="post-meta-item-icon"><svg class="icon" aria-hidden="true"><use xlink:href="#icon-calendar-line"></use></svg></span> <time title="创建时间：2020-07-18 16:23:52" itemprop="dateCreated datePublished" datetime="2020-07-18T16:23:52+08:00">2020-07-18</time><span class="post-meta-divider">-</span><span class="post-meta-item-icon"><svg class="icon" aria-hidden="true"><use xlink:href="#icon-calendar-2-line"></use></svg></span> <time title="修改时间：2021-02-01 13:52:11" itemprop="dateModified" datetime="2021-02-01T13:52:11+08:00">2021-02-01</time></div><span class="post-busuanzi"><span class="post-meta-divider">-</span><span class="post-meta-item-icon" title="阅读次数"><svg class="icon" aria-hidden="true"><use xlink:href="#icon-eye-line"></use></svg> <span id="busuanzi_value_page_pv"></span></span></span><div class="post-classify"><span class="post-category"><span class="post-meta-item-icon"><svg class="icon" aria-hidden="true"><use xlink:href="#icon-folder-line"></use></svg></span> <span itemprop="about" itemscope itemtype="https://schema.org/Thing"><a class="category" href="/categories/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C/" style="--text-color:var(--hty-text-color)" itemprop="url" rel="index"><span itemprop="text">计算机网络</span></a></span> > <span itemprop="about" itemscope itemtype="https://schema.org/Thing"><a class="category" href="/categories/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C/%E7%AC%AC2%E7%AB%A0/" style="--text-color:var(--hty-text-color)" itemprop="url" rel="index"><span itemprop="text">第2章</span></a></span></span><span class="post-tag"><span class="post-meta-divider">-</span><a class="tag" href="/tags/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C/" style="--text-color:blue"><span class="post-meta-item-icon"><svg class="icon" aria-hidden="true"><use xlink:href="#icon-price-tag-3-line"></use></svg></span><span class="tag-name">计算机网络</span></a></span></div></div></header><section class="post-body" itemprop="articleBody"><div class="post-content markdown-body" style="--smc-primary:black;"><h2 id="学习内容"><a href="#学习内容" class="headerlink" title="学习内容"></a>学习内容</h2><blockquote>
<ol>
<li>通信基础</li>
<li>两个公式 lim （重点）</li>
<li>看图说话</li>
<li>传输介质</li>
<li>物理层设备</li>
</ol>
</blockquote>
<h2 id="物理层基本概念"><a href="#物理层基本概念" class="headerlink" title="物理层基本概念"></a>物理层基本概念</h2><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718043631539.png" alt="" loading="lazy"></p>
<blockquote>
<p>接口（定义标准）</p>
</blockquote>
<h3 id="机械特性"><a href="#机械特性" class="headerlink" title="机械特性"></a>机械特性</h3><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718043223747.png" alt="" loading="lazy"></p>
<h3 id="电气特性"><a href="#电气特性" class="headerlink" title="电气特性"></a>电气特性</h3><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718043350719.png" alt="" loading="lazy"></p>
<h3 id="功能特性"><a href="#功能特性" class="headerlink" title="功能特性"></a>功能特性</h3><blockquote>
<p>电平表示何种意义</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718043533571.png" alt="" loading="lazy"></p>
<h3 id="规程特性"><a href="#规程特性" class="headerlink" title="规程特性"></a>规程特性</h3><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718043559507.png" alt="" loading="lazy"></p>
<h2 id="数据通信基础知识"><a href="#数据通信基础知识" class="headerlink" title="数据通信基础知识"></a>数据通信基础知识</h2><h3 id="典型的数据通信模型"><a href="#典型的数据通信模型" class="headerlink" title="典型的数据通信模型"></a>典型的数据通信模型</h3><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718043907852.png" alt="" loading="lazy"></p>
<blockquote>
<p>调制解调器 mao</p>
</blockquote>
<h3 id="数据通信相关术语"><a href="#数据通信相关术语" class="headerlink" title="数据通信相关术语"></a>数据通信相关术语</h3><blockquote>
<p>通信的目的是传送消息<br>数据 ：传送信息的实体，通常是有意义的符号序列<br>信源</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718044222215.png" alt="" loading="lazy"></p>
<h3 id="三种通信方式"><a href="#三种通信方式" class="headerlink" title="三种通信方式"></a>三种通信方式</h3><blockquote>
<p>1.单工通信<br>2.半双工通信<br>3.全双工通信</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718044357347.png" alt="" loading="lazy"></p>
<h3 id="两种数据传输方式"><a href="#两种数据传输方式" class="headerlink" title="两种数据传输方式"></a>两种数据传输方式</h3><blockquote>
<p>1.串行传输    远距离<br>2.并行传输    近距离（计算机内部）</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718044632450.png" alt="" loading="lazy"></p>
<h2 id="码元，波特，速率，带宽"><a href="#码元，波特，速率，带宽" class="headerlink" title="码元，波特，速率，带宽"></a>码元，波特，速率，带宽</h2><h3 id="码元"><a href="#码元" class="headerlink" title="码元"></a>码元</h3><blockquote>
<p>1 码元可以携带多个比特的信息。<br>例如 ， 2进制编码时，只有两种不同的码元，一种0状态. 一种1状态<br>4进制码元 00 01 10 11 （4种高低不同的信号波形）</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718045429618.png" alt="" loading="lazy"></p>
<h3 id="速率，波特，带宽"><a href="#速率，波特，带宽" class="headerlink" title="速率，波特，带宽"></a>速率，波特，带宽</h3><blockquote>
<p>速率 ： 码元传输速率 ， 信息传输速率<br> 码元传输速率 ：1s 传输多少个码元<br> 1 Baud(波特) = 1 码元/ s<br>信息传输速率 ：1s 传输多少比特</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718045920302.png" alt="" loading="lazy"><br><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718050025372.png" alt="" loading="lazy"></p>
<h3 id="练习题"><a href="#练习题" class="headerlink" title="练习题"></a>练习题</h3><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200718050318149.png" alt="" loading="lazy"></p>
<blockquote>
<p>8000/4<br>4进制 2位 2000<em>2<br>7200/6  1200</em>4</p>
</blockquote>
<h2 id="奈氏（nice）准则-香农定理"><a href="#奈氏（nice）准则-香农定理" class="headerlink" title="奈氏（nice）准则 香农定理 ***"></a>奈氏（nice）准则 香农定理 ***</h2><h3 id="失真"><a href="#失真" class="headerlink" title="失真"></a>失真</h3><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200720041622025.png" alt="" loading="lazy"></p>
<blockquote>
<p>1.码元传输速率<br>2.信号传输距离<br>3.噪音干扰<br>4.传输媒体质量</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200720042039316.png" alt="" loading="lazy"></p>
<blockquote>
<p>信道带宽：信道能通过的最高频率和最低频率之差<br>码间串扰：接收端收到的信号波形失去了码元之间清晰界限的现象</p>
</blockquote>
<h3 id="奈氏准则-奈韦斯特定理（为了避免码间串扰）"><a href="#奈氏准则-奈韦斯特定理（为了避免码间串扰）" class="headerlink" title="奈氏准则 奈韦斯特定理（为了避免码间串扰）"></a>奈氏准则 奈韦斯特定理（为了避免码间串扰）</h3><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200720042639841.png" alt="" loading="lazy"></p>
<blockquote>
<p>码元传输速率限制</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200720042725050.png" alt="" loading="lazy"></p>
<h3 id="香农定理"><a href="#香农定理" class="headerlink" title="香农定理"></a>香农定理</h3><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200720043404138.png" alt="" loading="lazy"></p>
<blockquote>
<p>信噪比（dB）= 10 log10（S/N）<br><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200720043547901.png" alt="" loading="lazy"></p>
</blockquote>
<h3 id="练习"><a href="#练习" class="headerlink" title="练习"></a>练习</h3><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200720043722693.png" alt="" loading="lazy"></p>
<blockquote>
<p>30db = 10 log10 (s/b)  s/b =1000</p>
</blockquote>
<h2 id="nice-与-香浓"><a href="#nice-与-香浓" class="headerlink" title="nice 与 香浓"></a>nice 与 香浓</h2><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200720044212093.png" alt="" loading="lazy"></p>
<p><img src="/images/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E7%AC%94%E8%AE%B0%E7%AC%AC/20200720044212093.png" alt="20200720044212093" loading="lazy"></p>
<blockquote>
<p>取较小的</p>
</blockquote>
<h2 id="编码与调制"><a href="#编码与调制" class="headerlink" title="编码与调制"></a>编码与调制</h2><h3 id="基带信号与宽带信号"><a href="#基带信号与宽带信号" class="headerlink" title="基带信号与宽带信号"></a>基带信号与宽带信号</h3><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200721041538681.png" alt="" loading="lazy"></p>
<blockquote>
<p>基带信号： 数字信道（基带传输）<br>宽带信号： 模拟信道（宽带传输） 把信号 调制<br>传输距离近，计算机网络采用 基带传输方式<br>远， 采用 宽带传输</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200721041854809.png" alt="" loading="lazy"></p>
<h3 id="数字数据编码为数字信号"><a href="#数字数据编码为数字信号" class="headerlink" title="数字数据编码为数字信号"></a>数字数据编码为数字信号</h3><p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200721043827157.png" alt="" loading="lazy"><br><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200721042205901.png" alt="" loading="lazy"></p>
<blockquote>
<p>(1)非归零编码  高1低0</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200721042417009.png" alt="" loading="lazy"></p>
<blockquote>
<p>(4)归零编码</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200721042920386.png" alt="" loading="lazy"></p>
<blockquote>
<p>(5)反向不归零编码</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200721043545889.png" alt="" loading="lazy"></p>
<blockquote>
<p>(2)曼彻斯特编码  前高后低1 前低后高0 看具体题目规定<br>数据传输速率只有调制速率的1/2</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200721043805614.png" alt="" loading="lazy"></p>
<blockquote>
<p>(3)差分曼彻斯特 同1异0</p>
</blockquote>
<p><img src="https://gitee.com/li_zikang/lzk-image/raw/master/img/20200721043917491.png" alt="" loading="lazy"></p>
<blockquote>
<p>(6) 4B/5B 编码 编码效率为80%</p>
</blockquote>
<h3 id="数字数据调制为模拟信号"><a href="#数字数据调制为模拟信号" class="headerlink" title="数字数据调制为模拟信号"></a>数字数据调制为模拟信号</h3><blockquote>
<p>音频数字化<br>脉码调制  pcm</p>
</blockquote>
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